Emulsifiers are, as substances essential to modern life, used in various production processes such as a production process of the so-called detergents, and are also contained in various articles for daily use and various food products. Alkyl sulfates obtained via organic synthetic routes, polyoxyethylene-based low-molecular-weight synthetic emulsifiers, etc. have so far been used as such emulsifiers. However, it has already been pointed out that these hardly undergo microbial degradation and, once they are released into the environment, they will not undergo biodegradation but be accumulated in the environment, possibly causing environmental pollution. Coating compositions and the like so far used in the form of solutions in organic solvents also have the possibility of causing similar environmental pollution and, from the occupational-safety viewpoint as well, it is desired that water be used in lieu of the solvents in current use.
To cope with such situation, it is necessary to provide coating compositions and the like with a certain degree of viscosity so that, for instance, in utilization of coating compositions and the like, sagging at coated sites after application thereof may be prevented. Since, however, the emulsifiers in conventional use are insufficient in viscosity, further addition of a thickening agent is required; this makes the compositions in question more complicated, causing problems in production and/or economic problems.
Also available as emulsifiers to be applied to mammals are such synthetic emulsifies as sugar esters. From the safety viewpoint, however, the utilization of natural products is desirable and, for example, proteins such as casein, lipids such as lecithin and plant polysaccharides such as gum arabic are utilized as natural emulsifiers. Although these are high in emulsifying property, the solutions thereof are low in viscosity and, when left for a long period of time, they disadvantageously separate into an aqueous phase and an oil phase. To solve this problem, it becomes necessary to add these emulsifiers in increased amounts or use them in combination with such a thickening agent as xanthan for stabilization; thus, they have problems from the economic and/or production viewpoint. Gum arabic has another problem; since it is a plant-derived product, the production thereof depends on the climatic conditions and the like, and therefore it is difficult to ensure a stable supply thereof.
According to other patent specifications in which the use of polyalcohols in emulsions containing a carotenoid or vitamin is described, it is necessary to additionally use an alcohol such as ethanol (cf. Patent Document 1), a nonionic emulsifier such as a polyglycerol fatty acid ester (cf. Patent Document 2), or both of them (cf. Patent Document 3). However, alcohols and nonionic emulsifiers are not favorably applicable in many preparations, in particular for mammals or, generally, they are not approved for use in foodstuffs. Further, a method is known for the production of carotenoid emulsions based on glycerol or another polyhydric alcohol and to be enclosed in soft gelatin capsules (cf. Patent Document 4). However, the emulsifiers used in the examples of the document are similarly nonionic emulsifiers and a further drawback is that the contents of active substances are relatively low.
Coenzyme Q10, which is one of coenzyme Q species and also known as ubidecarenone or CoQ10, is known as a liposoluble substance and technologies for retaining the homogenization and soluble condition thereof has been developed. For example, fat emulsions treated in a Manton-Gaulin high-pressure homogenizer using nonionic emulsifiers such as polyethylene glycol and polyoxyethylene-hydrogenated castor oil-(20)-ether have been disclosed (cf. Patent Document 5). Further, emulsions for intravenous injection given a particle diameter of 0.5 to 300 μm by treatment with a vegetable oil such as soybean oil or a phospholipid emulsifier such as phosphatidylcholine have been disclosed (cf. Patent Document 6). However, the former method has a problem in that the fat emulsions are large in particle diameter and inferior in transparency. Further, the latter emulsions for intravenous injection are low in coenzyme Q10 content and, when the concentration is increased, the problem of poor storage stability arises. As far as water-soluble compositions containing coenzyme Q10 are concerned, it is demanded that no oil component be necessary for emulsification and no special conditions or no complicated steps be required in the production.
In food manufacturing processes, there is a creaming phenomenon problem; when a liposoluble natural product is added to foods to be subjected to heat treatment in production steps such as cans, the emulsion is destructed and the liposoluble natural product floats up to the surface. In an attempt made to clear up this problem, a sucrose-condensed ricinoleic acid ester and an alcohol are used for heat-resisting emulsification (cf. Patent Document 7). However, in cases where the heating conditions are severe, for example, in the case of retort treatment of canned coffee (generally 125° C., 20 minutes), even the above prior-art technology allows the destruction of emulsions and the occurrence of creaming as a result. An emulsifier more resistant to heat is thus demanded.
In the field of cosmetics, emulsifiers are used especially for rendering liposoluble ingredients such as liposoluble colorants applicable smoothly over the skin and for dispersing them uniformly in cosmetics. In this case, chemically synthesized emulsifiers are in frequent use, and the possibility of their causing various troubles when they are used for a long period of time by direct application to the skin has been pointed out; thus, in the field of cosmetics as well, an emulsifier highly safe and friendly to the skin has been demanded.
Bath additives are mainly composed of: hot spring-derived inorganic salts; or an alkali carbonate and an organic acid with a perfume, a colorant, a plant extract, and the like are incorporated into a composition generating carbon-dioxide gas in the bath. In recent years, the skin-care effect of bathing has attracted increasing attention and a number of proposals for bath additives producing a skin-care effect have been offered. The methods of producing a skin-care effect by means of bath additives include: incorporation of moisturizing components such as polyhydric alcohols, polysaccharides or milk constituents; incorporation of plant extracts alleged to have a skin-care effect; and incorporation of oils, for instance. However, water-soluble moisturizing components are dissolved in bath water to give a dilute solution, and therefore hardly remain on the skin, hence their effect is weak. The use thereof in increased amounts so that their effect can be expected may make the skin after bathing sticky and, in addition, is uneconomical, hence is inexpedient. On the contrary, the use of oils is an effective means for producing an effect and giving a feeling of use by using relatively small amounts and, generally, the type of bath additives is such that oils are emulsified in bath water by means of an emulsifier. However, there is a limit to the level of incorporation of oils; excessive addition levels make the preparations inferior in fluidity and cause troubles in making preparations and, therefore, an emulsifier effective at lower addition levels is required. On the occasion of bathing, water is used in large amounts and an emulsifier is required also in large amounts, so that a safety problem will presumably arise; therefore, a highly safe emulsifier is demanded.
For such reasons as mentioned above, nature-derived emulsifiers higher in safety than in the prior art are required. Thus, such biological material-derived emulsifiers as mentioned below have been reported. A substance resulting from fusion between mannose and a protein is contained in the cell wall of Saccharomyces cerevisiae and this is known to show emulsifying action (cf. Non-Patent Document 1). For preparing this substance in this case, cells must be disrupted and the procedure therefor is very troublesome; accordingly, the substance has not been put to practical use as yet. Candida lipolytica isolated from the environment by screening is known to produce, in the medium, a substance showing emulsifying action (cf. Non-Patent Document 2). In cultivating this species, the use of such a hardly soluble carbon source as hexadecane is required, whereas the substance obtained by using such a soluble carbon source as glucose shows only low emulsifying action; this is a drawback.
Such substances obtained from the culture fluids of microorganisms and having emulsifying action are called biosurfactants, and are advantageous because they are neither toxic to living organisms nor persistent in the environment. They can also be mass-produced by cultivation. However, while the safety of these biosurfactants is said to be high, the fungi producing them are originally obtained from the environment, for example soils or woods, by screening with the ability to highly utilize oils, for instance, as an indicator, that is, those materials have never been eaten by humans; therefore, such biosurfactants can hardly be said to be truly high in safety. Known as emulsifiers derived from yeasts which have been eaten by mankind are emulsifiers derived from yeasts belonging to the genus Saccharomyces or Kluyveromyces (cf. Patent Document 8). These are, however, obtained only after heat treatment of cells themselves and are not defined as ones obtained from culture fluids.
In the natural world, there exist various microorganisms and, among them, there are some having an unknown function and biosurfactant-producing fungi have also been reported, and a certain number of biosurfactants such as surfactins and rhamnolipids (cf. Non-Patent Document 3) and sophorolipids (cf. Non-Patent Document 4) have already been put to practical use as a result of increases in productivity thereof. However, these biosurfactant producers are fungi isolated from the environment, typically soils, and whether they have actually been eaten by mankind or not is unknown; hence, they can hardly be said to be truly safe. Among the biosurfactants known in the art, sophorolipids are yeast-derived ones; however, they are of the glycolipid type from the surfactant-classification viewpoint, and the producers thereof, namely Candida bombicola, are taxonomically different from the yeast species to be used in the practice of the present invention and are not ones isolated from sources which have been eaten by mankind.
Patent Document 1: Japanese Kokai Publication S47-25220
Patent Document 2: Japanese Kokoku Publication S61-260860
Patent Document 3: Japanese Kokoku Publication S60-000419
Patent Document 4: Japanese Kokoku Publication S58-128141
Patent Document 5: Japanese Kokai Publication S60-199814
Patent Document 6: Japanese Kokai Publication S61-56124
Patent Document 7: Japanese Kokai Publication H04-299940
Patent Document 8: Japanese Kokai Publication H10-98
Non-Patent Document 1: D. R. Cameron et al., Applied and Environmental Microbiology, June 1988, 54, 6: p. 1420-1425
Non-Patent Document 2: M. C. Cirigliano et al., Applied and Environmental Microbiology, October 1984, p. 747-750
Non-Patent Document 3: M. Benincasa et al., 2002, J. Food Eng., 54: 283-288
Non-Patent Document 4: M. Deshpande and L. Daniels, 1995, Bioresour. Technol., 53: 143-150